1. Field of the Invention
The present invention relates to the field of earth boring tools and more particularly to tools used in a drill string incorporating diamond elements.
2. Description of the Prior Art
During a drilling operation, it is not uncommon for the bore being drilled to change, in time, from the diameter, shape and nature originally bored or for the bore to include bent or crooked sections. The rock formation often sluffs, swells, cakes up with hard deposits of drilling mud, slips or forms a key seat, all of which changes unavoidably either occur through the erosion or action of the drilling mud pumped down and then up through the bore, or by natural processes and events in the rock formation triggered in whole or in part by the disturbance in the formation caused by the drilling operation.
It is almost always necessary during drilling operations to trip out or remove the drilling bit which is typically attached at the lower end of a long drill string comprised of multiple 30 foot sections of pipe. In a bore not subject to any of the above changes or imperfections, the removal of the drill string and bit from the bore presents no problem, particularly in view of the fact that a perfect bore is drilled by the bit so as to have a diameter greater than the outer diameter of any other element included within the drill string. The bit thus will be the largest diameter element included within the drill string and will therefore easily slip fit out of a perfect, stable bore.
However, if in any event, any change or imperfection should arise in the bore to cause the diameter of the bore to become restricted or to introduce a sharp curvature in the bore, the bit or drill string can become wedged or jammed at the restriction or dog leg. Often, the drill string becomes so tightly jammed or seized within the bore that the drill string must be dismantled as much as possible, usually by detaching and removing that portion of the drill string above the jammed section or fish, and the fish must then be retrieved using special retrieving tools and techniques. Such a fishing operation is often extremely time-consuming and difficult, and when it occurs it can add substantial cost to the drilling operation. In fact, in some cases, retrieval of the fish is practically impossible and the hole must be redrilled around the fish which is permanently left in the bore.
Since, as described above, the bit is typically the largest diameter object in the drill string, many such jams occur when the bit becomes wedged at a constriction in the bore. In an attempt to facilitate removal of such jammed bits, the upper surface or chamfer of the bit, particularly in drag bits, have been provided with cutting elements including both natural and polycrystalline diamond elements to allow the bit to ream as it is rotated in the upward direction. Thus, when the bit is pulled up the bore, it jams against a bore restriction, the bit is rotated to ream out the constriction thereby freeing the bit to be withdrawn through the previously constricted section of the bore. However, the provision of a cutting face on the upper surface of the bit adds to the expense of manufacture and diamond material which is included within the bit, whether or not the up-drilling capacity of the bit is ever used. Thus, when a stable and problem-free bore is drilled, and the bit worn out, the unused up-drill portion of the bit is necessarily junked with the bit even though completely unused. Thus, expense is added to the cost of manufacture of the bit without any necessary increase in realized utility.
Moreover, in many cases, the drill string will jam within the bore at a dog-leg or key seat against a portion of the drill string while the bit remains essentially free. In such a case, an up-drill reaming face on the bit is totally ineffective and useless for unjamming seizure on the drill string at a distant location.
In addition, such up-drill faces on the bit have cutters with clearance of 0.105" and less, so that reaming action of such faces is minimal in many cases and is necessarily limited by the overall design of the bit. For example, such up-drill faces are not adaptable to conventional roller cone type bits.
Therefore, what is needed is a drilling tool which can ream or free a jammed bit and drill string at any location along the drill string, which can be simply used using ordinary kinds of operating procedures, which is rugged and simple of construction, which is reuseable independent of the drill bit, which may be periodically worn and replaced, and which is independent of drill bit design.